2 weeks ago before I went on holiday one of my 3 hives was bursting with bees. When I returned it was far less busy, but had not swarmed, as the queen is still there with no QCs and plenty of BIAS. But there are big piles of dead bees under and in front of the hive, as there are also in front of the other 2 otherwise healthy hives.
I have another hive 1/2 mile away that has also piles of dead bees but is otherwise healthy.
Could they be old winter bees (not noticed though in previous years) or maybe insecticide being used somewhere?
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